HbA1c Test Explained: Normal Range, Targets and What Your Result Means

The HbA1c test, also called glycated haemoglobin or A1c, is the most important blood test for diagnosing diabetes and judging how well it is controlled. Unlike a finger-prick reading, which shows your sugar at one moment, HbA1c shows your average blood sugar over the past two to three months.

How the test works

Glucose in the blood sticks to haemoglobin, the protein in red blood cells that carries oxygen. The more sugar in the blood, the more haemoglobin becomes "glycated". Red cells live about 120 days, so the percentage of glycated haemoglobin reflects average sugar over that time, with the most recent month contributing the most. A small blood sample from a vein, and sometimes from a finger-prick device, is enough, and fasting is not needed.

HbA1c ranges

• Normal: below 5.7% (39 mmol/mol)
• Prediabetes: 5.7-6.4% (39-47 mmol/mol)
• Diabetes: 6.5% (48 mmol/mol) or higher

Diabetes is normally confirmed by a second abnormal test, unless the person has clear symptoms and a very high glucose.

Two units: percentage and mmol/mol

HbA1c is reported either as a percentage (NGSP/DCCT units, used in the US and many labs) or in mmol/mol (IFCC units, used in the UK and increasingly in Sri Lanka). For example, 6.5% equals 48 mmol/mol, 7% equals 53, 8% equals 64 and 9% equals 75.

HbA1c and average blood sugar

HbA1c can be converted into an estimated average glucose (eAG) using the formula eAG (mg/dL) = 28.7 × HbA1c − 46.7. Examples:

• HbA1c 6% corresponds to about 126 mg/dL (7.0 mmol/L)
• 7% is about 154 mg/dL (8.6 mmol/L)
• 8% is about 183 mg/dL (10.2 mmol/L)
• 9% is about 212 mg/dL (11.8 mmol/L)
• 10% is about 240 mg/dL (13.3 mmol/L)

Our HbA1c calculator does this instantly. The eAG is an average, so your actual readings will swing above and below it.

Targets for people with diabetes

For many non-pregnant adults, a target HbA1c below 7% (53 mmol/mol) lowers the risk of eye, kidney and nerve complications. Targets should be individual:

• Tighter (6.5% or lower) may suit younger, healthy people with recent diabetes who are not at risk of low sugars.
• Looser (7.5-8.5%) may suit older adults, people with advanced complications, severe low sugars or limited life expectancy.
• Children and teenagers with type 1 diabetes often aim for below 7%.

Every 1% drop in HbA1c meaningfully reduces complication risk, so progress matters even when you have not reached the target. See typical day-to-day targets in our guide to normal blood sugar levels.

How often to test

• Newly diagnosed or changed treatment, or above target: every 3 months.
• Stable and at target: every 6 months.
• Prediabetes: at least yearly.
• Pregnancy: HbA1c is less useful; frequent glucose checks are used instead.

What can make HbA1c unreliable

• Anaemia: iron, B12 or folate deficiency can raise HbA1c; haemolytic anaemia and recent bleeding can lower it.
• Thalassaemia and haemoglobin variants, which are relatively common in Sri Lanka, may give false results with some lab methods.
• Chronic kidney or liver disease.
• Recent blood transfusion, which makes the result unreliable for about three months.
• Pregnancy, because red cell turnover changes.
• Some medicines, such as high-dose vitamin C or E, and certain HIV drugs.

If your HbA1c does not match your glucose readings, ask your doctor about other tests such as fructosamine or continuous glucose monitoring.

Improving your HbA1c

1. Take medicines exactly as prescribed, and ask about adjustments if readings stay high.
2. Follow a balanced diet, with controlled portions of rice and starch.
3. Exercise most days, including a walk after meals.
4. Check glucose at the times your doctor advises, and bring the log.
5. Reduce stress, sleep well and avoid smoking.
6. Treat high blood pressure and cholesterol too, because the aim is to prevent complications, not just to lower one number.

Do not try to cut HbA1c rapidly with crash dieting or by skipping medicines. Very fast drops may worsen eye disease in some people and increase low sugar risk.

HbA1c and time in range

People using continuous glucose monitors may also see "time in range", usually the percentage of time spent between 70 and 180 mg/dL (3.9-10.0 mmol/L). It complements HbA1c by showing swings in sugar that the average hides.

When to see a doctor

Ask about HbA1c testing if you are 30-35 or older, overweight, have a family history of diabetes, or have symptoms such as thirst and frequent urination. If you have diabetes, discuss your result and target at every visit. See also early symptoms of diabetes and how to reverse prediabetes.

References

• American Diabetes Association: Standards of Care in Diabetes, glycaemic goals and diagnosis
• Nathan et al., Diabetes Care, 2008: translating the A1C assay into estimated average glucose
• International Federation of Clinical Chemistry: HbA1c standardisation
• World Health Organization: use of glycated haemoglobin in the diagnosis of diabetes